The present invention generally relates to the field of dental instrument and more particularly, to shanks which can be fitted on contra-angles or handpieces such as, for example, instruments which are used in endodontics or in dental prophylaxis. The present invention also relates to heads for dental instruments which are equipped with such shanks.
At present, dental instrument shanks intended for use on contra-angles generally conform to the definition given under International Standard ISO 1797, for type 1 shanks.
For rotary driving, a type 1 shank according to ISO 1797 has a flat part which cooperates with an associated shape in the rotating elements of the contra-angle. This combination has the disadvantage of obliging the user, when fitting the instrument on the contra-angle, to seek an appropriate position shank so that the flat part engages the complementary shape of the rotating elements of the contra-angle. In practice, thus is not always easy to do particularly when the user is wearing gloves.
Moreover, the availability of new treatment techniques, particularly in the field of endodontics, has led to the application of greater torques than in the past. This has result in of this is an increased risk of deformation of the flat part, or of breaking of the shank.
In the case of disposable contra-angles, or those with a disposable head (e,g. as are described in the French Patent Application published under No. 2,692,473), the use of a type 1 shank according to standard ISO 1797 has made it necessary to provide a mechanical member in the head of the contra-angle, referred to hereinafter as a "cartridge", for receiving the rotary movement of the kinematic element of the contra-angle. The cartridge receives the shank of the instrument in an axial recess and presents the complementary shape necessary for being driven by the flat part of the shank.